Characterization of Ellipsoid and Interdigitation Zone Integrity in Retinitis Pigmentosa

Abstract

Purpose : Retinitis pigmentosa (RP) is an inherited retinal dystrophy characterized by nyctalopia and classic examination findings including peripheral bone spicules, arteriolar attenuation, and waxy optic disc pallor. Visual function correlates with the degree of outer retinal loss, especially of the interdigitation zone (IZ), ellipsoid zone (EZ), and external limiting membrane. This study seeks to further understand the structure-function relationship of the outer retina and characteristics at presentation affecting visual function.

Methods : Retrospective chart review was performed on patients with a clinical diagnosis of RP. Demographic and clinical variables were recorded. Optical coherence tomography (OCT) images were analyzed for the presence or absence of the IZ, EZ, and cystoid macular edema (CME). LogMAR visual acuity was the primary outcome and compared between patients presenting at age younger than 20 years, age 20-40 years, and those older than 40 years of age.

Results : Eighty eyes from 41 patients were included. There were 13 eyes in the age <20 group, 22 eyes in the age 20-40 group, and 45 eyes in the age > 40 group. LogMAR VA in these three groups was 0.47 ± 0.36, 0.41 ± 0.59, and 0.88 ± 0.93 respectively, and there was no statistically significant difference in logMAR VA between the groups (Kruskal-Wallis, p=0.074). There was significantly higher presence of IZ in the age 20-40 group compared to those >40 (χ², p=0.009); presence of EZ and CME were not significantly different between all groups (Figure 1). When comparing VA between eyes with presence of interdigitation zone and ellipsoid zone (+IZ/+EZ; 29 eyes), versus eyes with absence of interdigitation zone but presence of ellipsoid zone (-IZ/+EZ; 30 eyes), those with IZ present had significantly better visual acuity (0.22 ± 0.26 [Snellen equivalent 20/33] versus 0.42 ± 0.45 [Snellen equivalent 20/53]), p=0.036).

Conclusions : Presence of both the interdigitation zone and ellipsoid zone is associated with better visual acuity in patients with retinitis pigmentosa. The oldest patients had lower frequencies of present IZ, possibly due to more progressed, late-stage disease in those over age 40 upon initial presentation.

This abstract was presented at the 2024 ARVO Imaging in the Eye Conference, held in Seattle, WA, May 4, 2024.

 

Figure 1. Frequency of features on OCT versus age group. * denotes statistical significance after Bonferroni correction (p=0.009). EZ: ellipsoid zone; IZ: interdigitation zone; CME: cystoid macular edema.